Discovery Insure Rental Car Policy - Inconceivable

So after a bitter traumatic experience where hijackers tried to ***** my Fortuner and just a few days before me and 4 girlfriends will be going on a long awaited getaway (road trip) the ******* “luckily” only managed to cause damage to the vehicle resulting in it having to be towed for repairs. Up to this point everyone involved with reporting, registering the claim, towing the vehicle etcetera was patient, helpful and understanding. Now this is where everything changed as my rental clause kicked in and Avis informed me that, as per my contract, Discovery will cover the rental of a Renault Kwid for 30 days but that I am welcome to upgrade to a larger vehicle category (if required). Should I do so I have to pay the rental fee for the full 30 days (Max nr. of days as per my contract) in advance. If I upgrade to a Fortuner or a similar vehicle I will need to prepay R27 000 upon collection of the vehicle (daily upgrade rate of R900 per day for 30 days) because that's what my policy specify and that any credits will be refunded should I return the vehicle earlier but that they cannot upgrade the category for a shorter period than 30 days.

It's inconceivable that I insured a Fortuner and 2 other vehicles with Discovery for R3 200 per month but I need to prepay R27 000 in order to upgrade to a higher category, for a full 30 days or nothing. Not to mention how 5 friend all with luggage will be going on a road trip in a Renault Kwid.! Very frustrating and disappointing.